1. Field of the Invention
The present invention relates to an image processing apparatus, an image processing method, and a recording medium recorded with an image processing program. More particularly, the present invention relates to an image processing apparatus, an image processing method, and a recording medium recorded with an image processing program to process an image taking into consideration difference in the pickup condition of a face image using an AAM (Active Appearance Model).
2. Description of the Related Art
As a method of synthesizing a natural face image by analyzing statistically many face images without using a three-dimensional shape, Cootes et al. of University of Manchester have proposed a method using an AAM. The method using an AAM includes the steps of extracting shape information and texture information from the position, grey-level value and the like of landmark points defined for each feature of the face from a large number of two-dimensional face images, applying principal component analysis on each of the plurality of extracted shape information and texture information, and obtaining an orthonormal coordinate system (image space) corresponding to change in the shape and face expression, and altering the parameters along respective coordinate axes of the obtained image space to synthesize a face image. When an AAM is employed in an image recognition method, the parameters are altered within an obtained image space to synthesize an image. The parameters of the synthesized image that has the smallest difference from the face image that is the subject of recognition are obtained. By measuring the distance from the landmark vector of a face image that is already registered with the obtained parameters, recognition is made whether the image matches or not.
Japanese Patent Laying-Open No. 6-168317 discloses an individual identification apparatus taking into account inclination of the face. According to this individual identification apparatus, the position information of the landmark point of a face image is obtained to calculate the leftwards and rightwards rotation angle on the basis of the obtained position information and depth information of a reference face model. The position information of the landmark point is corrected so that the rotation angle becomes zero according to the obtained rotation angle and depth information. The individual identification process is carried out using the corrected landmark points. This individual identification apparatus can prevent reduction in the recognition rate of an input face image even if there is rotational difference leftwards or rightwards (the direction of turning the neck horizontally) between the face image that is registered in advance and the input face image.
The foregoing AAM employs a two-dimensional image. It is to be noted that shape information corresponds to the two-dimensional coordinates of a landmark point defined for each feature of a face. There was a problem that, from the extracted shape information, difference in the inclination of the face image in the depth direction could not be made such as whether the two-dimensional face image corresponds to a face oriented frontwards, upwards, or downwards. For example, the two-dimensional face image of a person with a wide forehead will be represented with a small forehead when the face is inclined upwards. If distinction of the face image in the depth direction cannot be made, the shape information extracted from the two-dimensional face image will erroneously represent the shape of a person with a small forehead.
The art disclosed in the foregoing Japanese Patent Laying-Open No. 6-168317 can accommodate difference in the rotation angle of the face in the horizontal direction in image recognition. However, there was a problem that upward or downward rotation, i.e. inclination in the depth direction, could not be accommodated.
As to an image obtained by shooting in a dark place and an image obtained by shooting in a light place, the object, even though identical, will be represented in different colors in the image. To remove this difference in the illumination condition, normalization of the light intensity was effected conventionally. In that case, there was a problem that difference in the color of the skin could not be identified. In other words, there was a problem that the tendency of the characteristic feature of a face arising from difference in nationality could not be extracted.